How is your memory usage when these issues are ocurring? You can determine this by opening Task Manager - Press Control + Alt + Del and click "Start Task Manager" it will tell you your current Physical Memory Usage. If it's higher than 75%, I would recommend using the MSCONFIG utility to disable uneeded startup items.
In order to do this, go to Start > Type in "MSCONFIG" and press enter. Once MSCONFIG is open, go to the "Startup" tab and uncheck all uneeded Startups (Anything that isn't a driver
or a Microsoft application*) then press Apply and Ok. You will be prompted to restart, after you do this try your normal activity again and see if you notice any improvements.
*If you don't know what something is, Google it and ensure it's safe to uncheck. Basically all MSCONFIG does is stops those applications from starting with your system and sitting idle in the background hogging resources. It does not affect the actual usage of the program.